1. Field of the Invention
The present invention relates to a coil component in which deviations in inductance of the coil component are restricted to a narrow range when a material having large deviations in relative permeability is used for forming a magnetic substrate for a coil, a transformer, or other electronic component.
2. Description of the Related Art
A conventional type of coil component is disclosed in Japanese Unexamined Patent Publication No. 8-203737. This coil component prevents deterioration of electric characteristics caused by shrinkage of a green sheet, which is a magnetic substance, which occurs during a firing process, by means of interposing a non-magnetic layer (an insulation layer) having a coil pattern disposed thereon between a pair of magnetic substrates.
The conventional type of coil component, however, has a disadvantage. That is, overall inductance of the coil component varies greatly when a material having large deviations in relative permeability is used as a magnetic substrate material for the coil component. This is because many of the conventional materials for a magnetic substrate which have been on the market are of a type in which the relative permeability varies within a range of about xc2x130% from a standard value. Thus, the inductance of a coil component produced by such a material, similarly, varies within a range of about xc2x130% from a standard value.
To overcome the problems described above, the preferred embodiments of the present invention provide a coil component in which deviations in an overall inductance of the coil component is significantly reduced to fall within a range of about xc2x15%, by using a magnetic substrate material in which the relative permeability has deviations within a range of xc2x130% but is equal to or greater than a specified desired value.
According to a first aspect of preferred embodiments of the present invention, there is provided a coil component which includes a pair of magnetic substrates, non-magnetic layers and a coil, the non-magnetic plates and the coil being laminated between the magnetic substrates, wherein a relative permeability of a material of the magnetic substrates is set in such a manner that a combined magnetic resistance R1 of the magnetic substrates arranged to define a closed series magnetic circuit including the pair of magnetic substrates and the non-magnetic layers, and a combined magnetic resistance R2 of the non-magnetic layers have a relationship: R2 greater than R1.
In preferred embodiments of the invention, the use of a material, having a relative permeability of a specified desired value or more, as a magnetic substrate material allows R1 as the combined magnetic resistance of the magnetic substrates to be smaller than R2 as the combined magnetic resistance of the non-magnetic layers. If Rm represents the combined magnetic resistance of a magnetic resistance circuit of the coil component including magnetic substrates and non-magnetic layers and the combined magnetic resistance of the non-magnetic layers R2 is made much larger than R1 which is the combined magnetic resistance of the magnetic substrates, then even in the case of using a material having large deviations of a relative permeability xcexcR1 as a magnetic substrate material, the combined magnetic resistance of the coil component Rm is determined predominantly by the combined magnetic resistance of the non-magnetic layers R2, and Rm is not affected by fluctuations of the combined magnetic resistance of the magnetic substrates R1. Therefore, the inductance of the coil component does not change in any significant amount.
According to a second aspect of preferred embodiments of the present invention, in the case of using a magnetic substrate material having a relative permeability which varies within a range of about xc2x130% from a standard value, when an overall inductance of the coil component having a respective relative permeability of about +30% and about xe2x88x9230% is respectively indicated as L1.05 and L0.95, the relative permeability of the magnetic substrate material is set to the value that is not less than the relative permeability obtained when the ratio L1.05/L0.95 of the inductance is about 1.105. With this novel feature of this preferred embodiment of the present invention, even if a material of type in which a relative permeability xcexcr1 of a magnetic substrate material varies within a range of about xc2x130% is used, an overall inductance of the coil component varies from the average value only within a range of about +5% at most and about xe2x88x925% at least.
According to a third aspect of preferred embodiments of the present invention, R1/R2 which is the ratio of the combined magnetic resistance of the magnetic substrates R1 to the combined magnetic resistance of the non-magnetic layers R2 is preferably set to a value that is about 0.182 or less by using a formula:       1.05    0.95    =            R2      +              R1        /        0.7                    R2      +              R1        /        1.3            
The third aspect of preferred embodiments of the present invention is described based on the ratio of the combined magnetic resistance of the coil component, while the second aspect of preferred embodiments of the present invention is described based on the ratio of the inductance of the coil component. However, both of the aspects above provide the same results.
Other features and advantages of the present invention will become apparent from the following description of preferred embodiments of the present invention which refers to the accompanying drawings.